Topic Contents

Thyroid Hormones

Topic Overview

Thyroid hormones are made by the
thyroid gland. The thyroid gland makes and releases
two thyroid hormones: thyroxine (T4) and triiodothyronine (T3). Thyroid
hormones affect every cell and all the organs of the body. Too much thyroid hormone speeds things up and too little thyroid hormone slows things down. They:

Control the rate at which your body burns
calories (your metabolism). This affects whether you gain or lose weight.

Can slow
down or speed up your heartbeat.

Can raise or lower your body
temperature.

Change how fast food moves through your digestive
tract.

Affect muscle strength.

Control how quickly your
body replaces dying cells.

The pituitary gland and the thyroid gland work together. The
pituitary gland (located near the base of the brain) makes, stores,
and releases thyroid-stimulating hormone (TSH). When TSH is secreted by the
pituitary gland, it causes the thyroid gland to release more T3 and T4. A high TSH level means there isn't enough thyroid hormone, and a low TSH level means there is too much.

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